Surface structure and dimensional effects on the aerodynamics of an owl-based wing model

Klän, Stephan; Burgmann, Sebastian; Bachmann, Thomas; Klaas, Michael; Wagner, Hermann; Schröder, Wolfgang

doi:10.1016/j.euromechflu.2011.12.006

Cited by 31 publications

(26 citation statements)

References 19 publications

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“…Additionally, they tried to model these aeroelastic effects with computational flow simulation tools. As opposed to the observations made by Kroeger et al regarding the aerodynamic performance of owls, Klän et al 19 examined an owl-based airfoil and argue that the surface structure of the owl wing may contribute to an increase of the aerodynamic performance of the wing by decreasing or suppressing the separation bubble or by stabilizing it.…”

Section: Ib the Silent Flight Of Owlsmentioning

confidence: 91%

Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings

Geyer

Sarradj

Fritzsche

2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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The wings and feathers of most genera of owls show unique properties that are held responsible for the silent flight of the owls. This ability to fly silently has long been of interest for engineers, with the aim to transfer the basic noise reducing mechanisms to technical applications such as blades of fans and propellers. The present paper describes acoustic and aerodynamic wind tunnel measurements on prepared bird wings of different species, among them two silently flying species of owls, the barn owl (Tyto alba) and the tawny owl (Strix aluco). The different wings are characterized in the study as technical airfoils in terms of their acoustic and aerodynamic performance. The experiments took place in an aeroacoustic open jet wind tunnel using microphone array measurement technique and deconvolution beamforming algorithms. Simultaneously to the acoustic measurements, the lift and drag forces of the wings were captured using a six-component-balance. This study, which is a complementary study to the approach of performing flyover measurements on flying birds, further confirms experimentally that the silent owl flight is a consequence of the special wing and plumage adaptations of the owls and not a consequence of their lower flight speed only.

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Section: Ib the Silent Flight Of Owlsmentioning

confidence: 91%

Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings

Geyer

Sarradj

Fritzsche

2012

18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)

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“…The white bars represent a length of 400 µm for each image. 35 turbulent flow further upstream. Due to the earlier transition to turbulent flow, the boundary layer can withstand more severe pressure gradients caused by the curvature of the wing.…”

Section: Transition Control (Velvet)mentioning

confidence: 96%

“…The effectiveness of this mechanism was concluded to depend on the flight velocity. 35 In conclusion, it was found that the application of the artificial surfaces can influence the size of the separation bubble in such a way that the size of the separation region is reduced or at least stabilized. Thus, these current experimental findings indicate that the aerodynamic performance can be enhanced passively by the surface structure of owl feathers.…”

Section: Transition Control (Velvet)mentioning

confidence: 96%

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Owl Inspired Silent Flight

Bachmann¹,

Winzen²

2014

Handbook of Biomimetics and Bioinspiration

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Urbanization and the constant upgrade of airports and wind power plants have led to the need of innovative wing-designs and applications to reduce noise of aircraft and rotors. How efficiently noise can be reduced during flight is shown by owls. Owls evolved unique wing geometries, surface-and edge-features to reduce flight noise to a minimum. Wings of owls are huge in comparison to the body mass. This in combination with a specific profiling leads to a wing geometry that produces much lift even at low flight-speeds. A velvety surface texture reduces friction noise of feathers and influences the boundary layer of the wing to delay separation. Serrations at the leading edge and fringes at the trailing edge of each remex influence both lift control and noise production by reducing turbulent eddies. Further, fringes merge neighboring feathers at the spread wing to create a smooth surface. Finally, the dense and porous plumage which covers the whole body acts as an acoustic absorber that dampens noise at the point of production. The complete knowledge of the physical mechanisms underlying silent flight of owls could lead to a future wing design and to applications that reduce noise pollution for humans and nature.

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“…We turn to the latter issue in the next section. Klän et al [47,58] and Winzen et al [59,60] conducted experiments with several artificial velvet-like surfaces that mimicked the length and the density of the natural pennula (figure 6a). The softness of the artificial material was also chosen to be similar to that of the natural owl-wing surface.…”

Section: Serrationsmentioning

confidence: 99%

Features of owl wings that promote silent flight

et al. 2017

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Owls are an order of birds of prey that are known for the development of a silent flight. We review here the morphological adaptations of owls leading to silent flight and discuss also aerodynamic properties of owl wings. We start with early observations (until 2005), and then turn to recent advances. The large wings of these birds, resulting in low wing loading and a low aspect ratio, contribute to noise reduction by allowing slow flight. The serrations on the leading edge of the wing and the velvet-like surface have an effect on noise reduction and also lead to an improvement of aerodynamic performance. The fringes at the inner feather vanes reduce noise by gliding into the grooves at the lower wing surface that are formed by barb shafts. The fringed trailing edge of the wing has been shown to reduce trailing edge noise. These adaptations to silent flight have been an inspiration for biologists and engineers for the development of devices with reduced noise production. Today several biomimetic applications such as a serrated pantograph or a fringed ventilator are available. Finally, we discuss unresolved questions and possible future directions.

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Surface structure and dimensional effects on the aerodynamics of an owl-based wing model

Cited by 31 publications

References 19 publications

Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings

Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings

Owl Inspired Silent Flight

Features of owl wings that promote silent flight

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